John Richards Symposia

This study examined the quantitative characteristics of infant saccadic eye movements in infants from 17 to 26 weeks of age. The “main sequence” is a linear relation between saccade velocity and amplitude. The main sequence relation is generated by the brainstem areas that control oculomotor nerves. In this study the main sequence was examined when infants made a saccade from an initial stimulus to a distractor stimulus in the display. Change in heart rate, which is an index of attention, and the experimentally defined stimuli were examined together.

Infants ranging in age from 17 to 26 weeks (total N = 12) were presented with experimentally defined stimuli in a Sesame Street movie. The segmented scenes consisted of random scenes shown as filler and one of five scene changes: calibration, movement combinations, location switch, location/character switch, and additions. The scene changes were initiated by a button press by the experimenter when the infant was looking at the correct location. Once the infant attended to the initial stimulus, a button was pressed which presented the second scene. This was followed by another button press once the infant attended to the second stimulus. This occurred for 55 s trial lengths. The electrooculogram was used to measure saccadic eye movements and the electrocardiogram was used to measure heart rate and heart rate phases. The fastest velocity of the saccade and the total amplitude of the saccade were quantified.

The main sequence relation between saccade velocity and amplitude was found in this study. That is, the velocity of the saccade was positively correlated with the amplitude of the saccade. The effect of attention on the main sequence relation was also examined. The decreased main sequence slopes for all ages during sustained attention were significantly different from the slopes during stimulus orienting and attention termination. There was not a significant difference between the slopes for the heart rate phase types, stimulus onset and attention termination. During sustained attention, the main sequence slopes show that there is a difference between the oldest age group (26 weeks) and the younger ages (17 and 20 weeks). However, the slopes for 17 and 20 week olds were not significantly different during this phase type. Finally there were no real differences in main sequence slopes among the age groups during attention termination. These changes in main sequence slopes across phase types for the three age groups support the theory that the visual system continues to develop postnatally. These findings suggest that attention promotes the main sequence relation in infants.

Dr. John E. Richards - Conference Presentations